1. Field of the Invention
The present disclosure relates to an exhaust gas analyzing system for sampling a part of or a whole of exhaust gas, emitted from an internal combustion engine, which is diluted and analyzed. Further, the present disclosure relates to a pumping device preferably used in the exhaust gas analyzing system.
2. Description of the Related Art
In the related art, a measuring system for particulate matters (PM), contained in exhaust gas, has been proposed including, as shown in WO2010/007965A, a combination of PM collection, employing a PM collection filter, and continuous measurement for measuring a particulate diameter concentration or the like upon using an analyzer such as a diffusion charge sensor (DCS).
More particularly, such a measuring system allows an exhaust gas introduction pipe to divert and sample a part of exhaust gas, emitted from the internal combustion engine, which is introduced into a micro tunnel (a diluter) for dilution with dilution gas. Then, the measuring system causes diluted exhaust gas, diluted in the micro tunnel, to be introduced into the PM collection filter. Moreover, the measuring system has a diluted exhaust gas sampling pipe for sampling a part of diluted exhaust gas at an upstream side of the PM collection filter for introduction to the analyzer such as the diffusion charge sensor (DCS).
Here, the measuring system has a flow rate adjusting mechanism, such as an electromagnetic proportional valve, which is disposed in a dilution gas introduction pipe connected to the micro tunnel. Such measuring system controls the flow rate adjusting mechanism to perform diverting dilution control on the basis of a flow rate of exhaust gas emitted from the internal combustion engine. That is, the measuring system adjusts the flow rate of dilution gas to be introduced into the micro tunnel such that a ratio (diverting ratio) between the flow rate of exhaust gas, emitted from the internal combustion engine, and the flow rate of exhaust gas diverted and sampled by the exhaust gas introduction pipe becomes constant.
With the measuring system performing such diverting dilution control, the flow rate of diluted exhaust gas, sampled by the diluted exhaust gas sampling pipe, results in the occurrence of an error in performing diverting dilution control with degradation occurring in analysis precision. For this reason, the measuring system is configured to allow correction gas (for instance, air) to be returned to a downstream side of the PM collection filter at the same flow rate as the sampling flow rate of the diluted exhaust gas sampling pipe. More particularly, a correction gas introduction pipe is connected between the PM collection filter and a suction pump provided at the downstream side of the PM collection filter. The correction gas introduction pipe has a mass flow controller provided for controlling the flow rate of correction gas at the same flow rate as the sampling flow rate.
However, in order for correction gas to flow into the downstream side of the PM collection filter via the mass flow controller, a compressed air source (compressor) needs to be provided at an upstream side of the mass flow controller. This results in the occurrence of an issue with a difficulty in downsizing the measuring system.